Johns Hopkins University is revving up for a wider opening in Baltimore after a months-long clampdown to fight the pandemic. But undergraduate classes will remain online for the first week.

The College of William & Mary in Virginia and the University of Maryland at College Park won’t start teaching in person until the spring term is two weeks old. The University of North Carolina at Chapel Hill will hold off for three weeks.

These are but a few examples in the profound and continuing havoc that the coronavirus crisis has wreaked in higher education. The intensification of the pandemic in recent weeks, with viral infections and covid-19 hospitalizations surging nationwide, has unleashed a new wave of uncertainty.

“It still seems like 2020 to me,” University of Arizona President Robert C. Robbins said. “We are still in this fight. But we feel confident that we’ve learned a lot.”

The semester began last week at the public university in Tucson with all classes online except for “essential in-person” teaching, much of that in laboratories. Robbins is promoting a January viral “testing blitz” to help keep the campus safe.

By now, schools and students are accustomed to the flux after the pandemic abruptly emptied campuses last March and caused widespread upheaval at the start of the school year in August and September.

Weary of the disruptions, students yearn to return to the classroom.

“Nothing beats in person,” said Anthony Joseph, who is the student government president at William & Mary, a public university in Williamsburg.

The 21-year-old senior from Pemberton, N.J., hopes a couple of his classes will shift to face-to-face mode after the semester starts. He even dares to imagine a real spring commencement. “Students as a whole are craving some sort of community that we’ve lost,” he said.

Colleges are racing to restore a sense of togetherness after a fall semester held under extraordinary — and deeply isolating — public health restrictions. Some campuses were almost vacant. Others housed modest numbers of students but taught remotely. Some opened up residence halls more broadly and taught mostly in person. Many used “hybrid” techniques that blended online and face-to-face experiences.

The choices that schools make are pivotal to public health. Covid-19, the disease caused by the coronavirus, has killed more than 408,000 people in the United States. Variants of the coronavirus are threatening to accelerate its spread even as authorities are stepping up a national vaccination campaign.

On Jan. 8, the Centers for Disease Control and Prevention released a study of what happened at the outset of the fall semester in counties that are home to universities with at least 20,000 students. The report found that the incidence of infection tended to decline where schools taught remotely and rise where schools taught in person.

The CDC said schools can limit spread of the virus through measures such as mask-wearing, social distancing and expansion of viral testing. Regulating behavior outside the classroom is crucial: College and university leaders say the virus spreads much more off campus than in academic spaces.

In some places, universities are struggling to house students. California, now a viral hot spot, is a case in point. The state’s seven-day average of daily new cases stood at 81 per 100,000 residents as of Thursday. That was one of the highest totals in the nation, behind South Carolina’s total of 96 and Arizona’s of 105.

On Jan. 9, Stanford University ditched plans to invite first- and second-year students to live on campus for its winter quarter. “We are now at the worst point of the pandemic so far,” Stanford officials wrote as they lamented skyrocketing infections in California. On Jan. 11, the University of California announced it will aim for a systemwide resumption of in-person teaching next fall.

Christopher R. Marsicano, an assistant professor of the practice of higher education at Davidson College, who is tracking how schools nationally respond to the crisis, said most are sticking with plans developed last summer and fall. Some, he said, are delaying the start of the semester or the start of in-person teaching to buy time. They want to “pump the brakes a little bit and slow down,” he said.

The University of Oklahoma, in another hard-hit state, delayed the start of its spring semester by one week, to Jan. 25. It also will shrink the number of classes taught in person and expand viral testing. “The one thing I cannot control — no university can control — are the activities of the students outside of the classroom, after hours,” said Dale Bratzler, an infectious-disease and public health expert who is the university’s chief covid-19 officer. But he said Oklahoma officials are confident in their plans.

The University of Wisconsin at Madison, with some classes in person, made a similar schedule shift. The University of Virginia plans to start with some in-person classes Feb. 1. Last year, its classes started Jan. 13.

In Chapel Hill, UNC is seeking to avoid the embarrassment it suffered in August when the university abruptly scrapped in-person teaching days into the school year as viral cases spiked. Kevin M. Guskiewicz, chancellor of the university, recently ordered a three-week delay for the start of in-person teaching and allowed students to move into dormitories later than planned. “We all have learned a lot from the experience of the past fall,” he said. “The slower we can ramp up . . . the safer it will be for the surrounding community.” He is counting on masks, distancing and increased viral testing to control spread of infection.

Some remain skeptical. “New semester, same irresponsibility,” the editorial board of the Daily Tar Heel student newspaper wrote of UNC’s plans.

In D.C., American, Georgetown, George Washington and Howard universities will be mostly online. Catholic and Trinity Washington universities will have some in-person classes. The schools must contend with the added complication of heavy security in the capital in the aftermath of the Jan. 6 attack on the Capitol and the run-up to Wednesday’s presidential inauguration. Viral infections are surging in D.C., Maryland and Virginia, with more than 6,300 new cases reported Thursday.

Outside the city, U-Md. announced in December that the first two weeks of the semester will be online, a precaution that officials say will give the school time to conduct widespread viral testing and limit student movement.

Johns Hopkins University in Baltimore built a temporary structure on its freshman quad with ventilation to help students to gather, study and hold events. (John Hopkins University)

In Baltimore, about 1,250 undergraduates are moving into Johns Hopkins residence halls. More will be living nearby off campus for the semester that begins Monday. University officials plan a limited amount of in-person teaching. The one-week bump in the launch of that instruction, to Feb. 1, was meant to give adequate time to test students for the virus.

Because Johns Hopkins is renowned for public health expertise, much is riding on the university’s plans. Provost Sunil Kumar said the university relied heavily on its faculty and consulted with other universities. “At the end of the day, safety comes first,” he said. “If we do not have confidence that we can operate safely, of course we would shut down.”

The spring term opening in Williamsburg will be tightly choreographed. First-year students at William & Mary move in Saturday, seniors a week later, sophomores and juniors a week after that. Classes will start remotely Jan. 27, while any face-to-face teaching debuts Feb. 10. Dining halls will be all takeout at first, to maximize mask-wearing in places where students run into each other.

“You have to have enormous humility and enormous caution,” William & Mary President Katherine Rowe said. Her goal is to turn public health rules into habits. She said the university also will use gear such as tents and firepits to help students find ways to hang out safely outdoors.

“It sounds small, but it’s really not,” Rowe said. She knows the pandemic is taking a toll on emotional and mental health. “Students have found the isolation really, really challenging.”

Lauren Lumpkin contributed to this report.